Process for treatment of sulphate-containing water

A process for treating a raw water having anions comprising sulphur and oxygen dissolved therein, the process comprising the steps of:

• subjecting the anions comprising sulphur and oxygen to an anaerobic biological reduction whereby the anions comprising sulphur and oxygen are converted to sulphide (S=) anions to produce dissolved sulphide anions in the water;
• subjecting the sulphide anions, produced in the water by the anaerobic biological reduction, to a biological oxidation whereby the dissolved sulphide ions are oxidized to elemental sulphur to produce suspended elemental sulphur in the water;
• and
• separating from the water the suspended elemental sulphur produced in the water, the anaerobic biological reduction and the biological oxidation being effected simultaneously in the presence of each other in a series of common reaction stages in which there are oxidizing conditions which permit the biological oxidation to take place without preventing the anaerobic biological reduction from taking place, the process being carried out on a continuous basis, there being a continuous feed of raw water to the series of common reaction stages and the anaerobic biological reduction and the biological oxidation taking place continuously in the common reaction stages, water containing elemental sulphur and biomass being continuously withdrawn from the reaction stages and continuously fed to a sludge separation stage, separate from the reaction stages, where the continuous separation of the elemental sulphur, together with biomass, from the water takes place, the process including continuous recirculation of part of the separated sulphur and biomass, sufficient to maintain a suspended solids content in the reaction stages of 2-50 g/L, the water being treated being passed through said series of common reaction stages in each of which both the anaerobic biological reduction and the biological oxidation take place, and through said sludge separation stage at the end of the series, the process including recirculating water containing dissolved bicarbonate (HCO3−) anions from the sulphur separation stage to the reaction stages, thereby to cause a progressive rise in the pH of the water from reaction stage to reaction stage along the series in a downstream direction.